A glycolic acid (α-hydroxyacetic acid) has hitherto been used as a general purpose chemical product such as a detergent for boiler scale or the like. However, in recent years, it has been paid attention to as a raw material of polyglycolic acid useful as a material for cosmetics, a biodegradable polymer or a polymer for medical applications. For this reason, there has been increased demand to supply glycolic acid having a high purity at low cost.
A glycolic acid of the class which has been currently put on the market and industrially used is produced by the carbonylation reaction of formaldehyde and water in the presence of glycolic acid and sulfuric acid. The obtained crude glycolic acid has been purified through multi-stage steps such as decolorization by activated carbon treatment, removal of sulfuric acid by an anion exchange resin, removal of low-boiling contaminants by live steam stripping and removal of metallic contaminants by a cation exchange resin (Patent Document 1).
However, the glycolic acid obtained according to the method as described in Patent Document 1 contains not a little contaminants so that it has a problem as a raw material for cosmetics or a raw material for polymers in terms of the purity. For example, organic acids such as oxalic acid, formic acid and the like contaminate in the glycolic acid in some cases. When the glycolic acid is used as a raw material for polymers, even though these contaminants are contained in a very small quantity, a dehydrative condensation reaction of glycolic acid is inhibited and a high molecular weight of glycolic acid is relatively suppressed. Furthermore, a component for coloring polyglycolic acid into a black color is also contained in the contaminants. Furthermore, one of contaminants, methoxyacetic acid, is a compound that is suspected of carcinogenesis, and it is not desirable that methoxyacetic acid is contained in packing materials of cosmetics, food or drink.
In order to enhance the purity of glycolic acid, there has been disclosed a method including adding glycolic acid having a relatively high purity in a small amount as a seed crystal to the glycolic acid of an industrial class obtained in the foregoing purification method and carrying out cooling crystallization at 5 to −18 degree centigrade for obtaining glycolic acid with a smaller amount of contaminants (Patent Document 2). According to the method described in Patent Document 2, there has been described that glycolic acid having a purity of 99% or more may be obtained. However, there is a problem in that the yield is remarkably low (the yield is 6.6% at 5 degree centigrade).
Meanwhile, there has been described a technology that, when organic acid is produced according to the fermentation method by a microorganism, electrodialysis is conducted by an ion exchange membrane, a chelating resin treatment is performed after the electrodialysis, and a water-splitting electrodialysis is conducted by the ion exchange membrane after the chelating resin treatment to respectively collect organic acid and alkali (Patent Document 3).
However, in the Patent Document, there has been no description on useful polyglycolic acid as a material for cosmetics, a biodegradable polymer or a polymer for medical applications, and a raw material glycolic acid for obtaining the polyglycolic acid. Furthermore, when the glycolic acid obtained according to the method described in Patent Document 3 is also used as a raw material, the contaminants are not sufficiently removed, and a high molecular weight of the thus-obtained polyglycolic acid is suppressed.
Patent Document 1: U.S. Pat. No. 3,859,349
Patent Document 2: Japanese PCT International Patent Laid-open No. 1994-501268
Patent Document 3: Japanese Patent Laid-open No. 1997-135698